Integrated field effect circuitry



April 23, 1968 J. BLANLUET 3,379,941

INTEGRATED FIELD EFFECT CIRCUITRY Filed March 5, 1964 JW FIG 3 M 0W United States Patent 0 ice 2 Claims. 61. 317-235 ABSTRACT OF THE DISCLOSURE An integrated circuit comprises a substrate and over said substrate, a plurality of electric components, each connecting one point of the circuit to another. Each component is enclosed in the channel of a field efiect structure comprising a source, a drain and two gates. The channel is pinched olf by applying to the gates, source and drain, a convenient DC. potential, and insulates this component from the other parts of the circuit.

The present invention relates to integrated circuits.

As is well known, integrated circuits are built up by forming within the body of a semiconductor plate, pellet or wafer, for example a silicon plate or pellet, a number of layers having diiferent conduction characteristics which constitute the various components of the integrated circuit, such as transistors, resistances and others.

Under certain conditions, the problem may arise of defining the boundaries of a component on the surface of a semiconductor body, in other words of defining with great precisions the geometry of the component or components concerned.

To this end, it is known, to define the geometry of one component by diffusing into a semiconductor plate an impurity, whose conductivity type is the reverse of that of the remainder of the substrate.

However, it may be of interest to isolate within an integrated structure, elements having the same type of conductivity without any diffusion other than that which serves to form the other components of the integrated circuit.

It is an object of the invention to provide an improved integrated circuit wherein this problem is solved.

According to the invention there is built within the semi-conductor body within which the integrated circuit is formed, at least one field effect structure which, upon application to it of a blocking bias, is capable of forming within said body an insulating region of a predetermined geometry.

In particular, resistors can be formed in this Way in an integrated circuit.

The invention will be best understood from the following description and accompanying drawing, wherein:

FIG. 1 is a top view of a portion of an integrated circuit according to the invention;

FIG. 2 is a section through line ad of FIG. 1, in which the thickness of the structure has been considerably enlarged for clarity; and

FIG. 3 is the equivalent circuit of the arrangement shown in FIGS. 1 and 2.

The same reference numbers are used to designate the same parts in the different figures.

FIG. 3 shows the diagram of the circuit which it is desired to form, i.e. a field effect structure, whose respective gates are connected to terminals 2 and 3, whose source is grounded, and whose drain is coupled to a DC. supply 4 through a load resistor 5.

Said field effect component is formed in a conventional 3,379,941 Patented Apr. 23, 1968 manner, i.e. by means of a comparatively shallow difiusion within one face of a plate 6 of 11 type silicon from an epitaxial wafer.

This gives, on one face, a circular source 1 of m type, a circular gate 3 of p type and a circular drain 11 of n+ type and, on the other face, a p+ type layer which is gate 2.

According to the invention, a resistance 5 is obtained by determining a region of 11 type having a well defined geometry within the silicon body, by forming a field effect structure in the following manner.

A strip 8 of n+ type, and a strip 7 of p type are formed. Strip 7 surrounds the annular junction n+, that makes up the drain of the field effect component 1, and strip 8 an defines a channel 9, of length L and a width 1.

Region 8 serves as the drain of the above field effect structure, the region 11 playing the role of source, while regions 7 and 2 are the gates. In order for the set up to operate according to the invention it suflices that the field effect structure should be blocked. In other words, the potential applied to strip 7 must be negative with respect to region 6 potential; potential of region 8 being of course positive with respect to region 6 potential.

Under such conditions, the two semiconductor regions of n type located below portions 7a and 7b, operate as insulators. A region 9 of 11 type having a length L, a Width 1, and whose depth e equals that of layer n, is thus defined.

This region builds up a well defined resistor which is the resistor 5 of FIG. 3. It connects the drain of the field etfect transistor 1 to strip 8 biased by the D.C. supply 4.

Of course, the invention is not limited to the embodiment described and shown which was given solely by way of example.

Various integrated circuits may be devised including a field elfect structure according to the invention, and the field effect structure playing the role of insulator may be formed in various manners known to those skilled in the art.

The field efiect structure must be so formed that the leakage current in the blocked channel should be as low as possible.

The region which is relatively of the p type serving as gate for the field efiect structure can also serve in addition as a resistive element in the integrated circuit.

What is claimed is:

1. In an integrated circuit,

a semiconductor water of one conductivity type,

a first source region of said one conductivity type disposed in said wafer,

a first drain region of said one conductivity type disposed in said wafer adjacent said source region,

a first gate region of opposite conductivity type disposed in said wafer between said source and drain regions,

a second drain region of said one conductivity type disposed in said wafer at a given space from said first drain,

a second gate region of said opposite conductivity type disposed in said wafer in the form of a constricted loop so as to encompass all of the aforesaid regions with a constriction of said space to form in said wafer a channel region of said one conductivity type and having a significant characteristic of an electrical element, and

bias means connected to said source, and second gate region for completely pinching off said channel region to isolate said electrical element from said wafer.

2. An integrated circuit as claimed in claim 1, wherein said channel region has the characteristic of a resistor.

(References on following page) References Cited UNITED STATES PATENTS Buie 317-235 Doucette 307-885 Cook et a1 307-885 Brown et a1 307-885 XR Evans 307-885 Noyce 317 235 Matare 307-885 MacDonald 330-38 Evans et al. 307-885 Leger 307-885 Biard 317-235 Henkels 331-107 JOHN W. HUCKERT, Primary Examiner.

R. F. SANDLER, Assistant Examiner. 

